REPAIR: Zeiss Jena Flektogon 2.8/35mm (Praktina mount)

[stevemark]

Yesterday I got a rather worn (but working) K&W Praktina FX, together with three Praktina bayonet lenses, all in pretty bad condition. One of them was this Carl Zeiss Jena Flektogon 2.8/35mm:


Apart from being rather dirty, its focus is completely stuck (can't move it at all even with quite some force applied), and the aperture ring is stuck as well. The lens has the 2nd gen Flektogon bayonet with the ingenious "semi-automatic" aperture: You can focus with the aperture wide open, but after pressing the shutter button (and immediately before shutter release) the aperture is closing to its pre-selected value. That was huge thing when K&W introduced it around 1957. While the aperture rin is stuck at f3.5, the clocking mechanism and the aperture release actually are working, which is a good thing!


PART I - SEPARATING THE LENS INTO ITS FOUR MAIN COMPONENTS

Another good thing is that the front ring with ist engravings has two small incisions, ulinke most other CZJ lenses from that time frame I own. They allow for using a lens spanner, and the ring comes off pretty easily:


Next is the removal of the front lens group, using a lens spanner with a pointy end:



View into the lens after the removal of the front group. The retainer ring we can see clearly will beremoved later on.


Before that, however, we'll remove the rear lens group. Trying to remove the corresponding retainer ring I got into difficulties - it was completely stuck as well. Therefor I was soaking the ring with acetone ...


... and after a few minutes it became loose:



Now I was able to remove the rear lens group (plus a distance holder), quite badly fogged as you can see:


Removing the lager retainer ring in the above image (its two slits being close to the two large black screws) would separate the focusing mechanism from the aperture mechanism. That's a really clean and clear mechanical construction!


Now we have separated the lens in its four main components!


Upper left/center: Front ring and front block of the optics
Upper right: Rear block of the lens
Lower center: Fousing mechanism
Lower right: Aperture mechanism

Since both the focus as well as the aperture mechanism are COMPLETELY stuck, I decided to immerse them in acetone:


Good news: After a few hours - and with applying a fair amount of force! - the focusing mechanism became free. The aperture mechanism didn't need too much force; simply pushing the ring downwards (NOT turning it!!) would free it up. Before working on it I'll clean the optical groups, however.

[stevemark]

PART II - CLEANING THE FRONT AND THE REAR LENS BLOCK

Removing the retainer ring which retains the large negative front lens:



Removing the front lens itself (be careful not to remove or damage the blackening at its rims):


On the rear side of the front element, this retainer ring can be removed easily.


The lens element exposed now is a doublet, but it's kind of glued in (or at least fixed by the black color), so it didn't just come out as I would have expected:



Therefore I'm continuing from the front end, removing the next retainer ring which is hidden pretty deep inside the black conus:


The retainer ring and the corrresponding lens come out pretty easily (not shown here).

Next is dismantling the rear lens group which consist of two lenses:


After removing the retainer ring on one ...


... and the other side ...


... the entire rear group is now ready for cleaning:


Note that the two lenses of the rear group both are slightly yellowish - contributing to the warm rendering of this version of the CZJ 2.8/35mm (not all versions are the same!):


Typical for Zeiss (and Leica, if I'm right): Not only the barrel itself, but also the front as well as ther rear optical block are engraved / staped with the SN, thus preventing confusion and mix-ups when handling several "identical" lenses at a time.



BTW the numbers stamped into the real optical group (image above) are less than 1mm high and probably not much more than 0.5mm wide ...

Next step: dismantling, cleaning, re-lubing and reassembling the focusing mechanism.

[stevemark]

PART III - FOCUSING MECHANISM

Before dismantling the focusing mechanism I usually measure it:


The two rather large black screws are acting as guides for the focusing mechanism; removing them enables us to separate the two main parts of the mechanism:



These two black screws - rather large again - are acting as stoppers (infinity and MFD); removing them allows us to extract the front part of the focusing mechanism:



The silver screw as well as the prong can remain, at least fro time being:


Now we can carefully separate the two parts of the focusing mechanism. This is a bit tricky since the cocking lever for the aperture mechanism is interfering, but step by step (moving the lever / moving the threads / moving the lever ...) you'll succeed! Don't forget t mark the position of the separation:



Before unscrewing the next two parts we measure it again:


Now the two parts are separated as well:



The inner parts of the aperture cocking mechanism (everything is really dirty - lots of completely dried out grease)


Three screws connecting the lever and the aperture cocking mechanism (lelft side, partly covered):


Before we can remove the lever and the aperture cocking mechanism we must remove this metal ring (a kind of a spring):



Now the three screws connecting the lever with the aperture cocking mechanism are exposed, and we can remove them:



A very long spring is moving the shiny silver ring (aperture cocking mechanism):



Once the spring is extracted, wen can remove also the shiny silver ring (aperture cocking mechanism):



Now the small lever of the aperture cocking mechanism can be removed. ATTENTION: There's a small spring which easily can be lost!!



Now the entire focusing mechanism is dismantled and ready for cleaning:


Cleaning the old hardened Zeiss Jena grease is a real PITA. It's not even properly dissolving in acetone! To soften the gunky stuff I've been boiling it in water / detergent for half an hour or so. A susbtantial part of the old grease came off the lens parts, but I still had to clean them carefully using a teethbrush, lots of detergents, and hot water. After that the threads sill weren't clean enough, so I put them into acetone and cleaned them as good as poosible using Q-tips. Finally, polishing the aluminum surfaces was done with 1200 and 2500 grade polishing paper. Cleaning all the parts took probably two hours or so!!

But it was worth the effort:




The cleaned and re-assembled lens:


S

[stevemark]

Here's the repaired / re-lubed / cleaned CZJ Flektogon 2.8/35mm in Praktina mount, along with two other sample in M42 and Exakta mount:



S

[visualopsins]

Really nice work! Thank you so much for sharing. I have an M42 mount with stiff helicoid to hopefully repair.

[stevemark]